Telephone system



May 6 1924. v

P. LUBBERGER TELEPHONE SYSTEM s Sheets-Sheet 1- Filed June 5, 1923 F. LUBBERGER TELEFHONE SYSTEM Flled June 5 192:. s Sheets-Sheet 2 4 May 6 1924.

my I

May 6 1924. 1,492,995

F. LU BBERGER TELEPHONE SYSTEM Filed June 5. 1923 s Sheets-Sheet 5 When/0f.-

' fig Labia/yer, fly i 4/232 Patented May 6, 1924.

i'rsn s'r FRITZ LUIBBERGER, O'F SCHMARGENIDORE (S-lElllEtlVIANY, ASSIGNOR T fS IEMENS &

HALSKE, AKTIENGESELLSCHAFT, OFSIEMENSSTADT, NEAR BERLIN, GERMANY,

A CORPORATION OF GERMANY.

TELEPHONE SYSTEM.

Application filed June 5, 1923. Serial No. 643,520.

To all whom it may concern:

Be it known that I, FRITZ LUBBERGER, a citizen of Germany, residing at Schmargendorf, Germany, have invented certain new and useful Improvements in Telephone Sys tems, (for which I have filed application in Germany Number S. 59,685, May 9, 1922), of which the following is a full, clear, concise, and exact description. 1

This invention relates to telephone systems and particularly to that type of system in which machine switching devices are employed and further in which; separate speaking and setting routes are used.

The object of the invention is the provision of a flexible means for providing different classes of service.

Class of service arrangements in which the called lines are segregated in groups according to their classification have heretofore'been employed but to the best of applicants knowledge and belief no such system employing separate speaking and setting routes has been known.

It is therefore a further object of this invention to provide a class of service system in combination with a by-path machine switching telephone system.

A further object is to provide a system in which the class of service determination is a function of both the calling and the called mes.

A feature of the invention resides in a plurality of common conductors each maintained at a different but definite potential and to which the lines are differently connected. Each line in characterized by the connection of an incoming-and an outgoing lead maintained at a predetermined. potential. The class of service is then determined and the resulting operations are controlled through the connection of a calling lines outgoing lead through a common responsive device to the called lines incoming lead.

Thus all lines of a particular class are characterized by having an outgoing class of service lead of a particular potentialand an incoming class of'service lead of a particular potential, which may be higher, the M3 same or lower than the outgoing class of service potential. I

Another feature of this invention is the flexibility of the system, which lies in the fact that the class of service of any line may be changed by the simple expedient of changing-its individual connections to the common potential leads. x Q

Stillanother feature of this invention resides in the'results which arise from making the class of service determination a function of both calling and called ;line. Thus there may be one class of lines which may establish connectionsto all other lines regardless of their class and to which all other class lines, may establish connections. Again there may be lines which can only call andbe called intheir own class. Furtherthere may be lines which can calllines of all other classes but can only be called by lines of aparticular class. In fact the present'invention lends itself to a wide field of usefulness inasmuch as a large pluralityof classes of service, may beprovided with a very small amount of common apparatus and hence almost anyv particular class of service which may be desired is ready athand. Thus, as willbe fully explained hereinafter, with four potential leads there may be as many as sixteen separate and distinct classes of service and with five potential leads there may be twenty :five different classes of service-.- It. will thus be seen that the number of classes of service is the square of the number of potential leads. e 1 Another feature is the class of vservice responsive devicewhich comprises a simple polarized relay which for a single brief period during the establishment is serially included in .a circuit between the calling line outgoingclass of service potential lead i and the called line incoming class of service potential lead. If the potentials on these two leads areequalso that the relay does not energize or if they are unequal and so arranged to cause a flow of current in one directionso that the relay becomes energized and tendstomove its armature in-one direcv tion then the establishment of the connection is allowed to proceed but if the potentials on these two leads aresoarranged that'a flow ofv current in trimmer is caused then this r la z ee aeaerai ee tee t m armature in the other direction with results which prevent the establishment of the connection.

In the drawings Fig. 1 is a schematic representation of the essential elements of the present invention whil Figs. 2 and 3 taken together form a diagrammatic repre-- sentation of a telephone system employing the present invention.

Fig. 1 is a diagrammatic representation of the essential elements of the present invention. Each telephone line in a system employing this invention may be provided with a particular class of service by the arrangement of certain two class conductors associated therewith, one of which we will designate 0 for outgoing and the other of which we will designated fonincoming. Thus, in the figure, the hand circle with the heavy lines leading therefrom is intended to represent a telephone line provided with, say, class '1 service. This classof service is determined by the arrangement of its associated class conductors 0 and z'.

A plurality of conductors carrying dilierent potentials are provided common to all telephone lines to which the class conductors of the said lines are connected. Thus, conductor may be at zero potential, conductor '7 may be at 20 volts potential, conductor 8 may be at 40 volts potential and conductor 9 may be at 60 volts potential. In the case of line 1, the outgoing class con ductor 0 is connected to conductor 9 and the incoming class conductor 1' is connected to conductor 6.

In general, there are four classes of service provided, asrepresented by lines 1, 2, 3 and 4:, respectively, and such four classes will take care of all ordinary telephone requirements, but this invention is not limited to the provision of four classes. Thus. a fifth class is illustrated in connec tion with line 5, It will be understood that with the four potential leads and with the two class conductors for each line that the maximum number of different classes possible is sixteen, since one class conductor may be connected to any one of the four potential conductors and the other class conductor may be likewise connected to any one of the four potential conductors. Should there be, say, five potential conductors, then the maximum number of different classes of service which could be provided would be five times live or twenty-five.

Each telephone line has associated with it aprimary line switch by means of which the telephone line may be extended. There are also provided secondary line finder switches by means of which the telephone lines may be further extended. In Fig. 1 wiper 11 represents one of the wipers of the primary line switcl i associated" with line 1, and wiper 16 represents one of the wipers associated with a secondary line finder switch for further extending line 1. Thus, upon" the initiation of a call on line 1, the 0 class conductor of line 1 is extended through wiper 11 and thence over the first one of the idle trunk conductors illustrated to wiper 16 of the secondary line finder switch. Thereafter, the conductor 0 is extended through a polarized relay 17 to the brush 18 of a numerical switch. In a manner which will be described hereinafter, the numerical switch may be set in connection with any desired called line, whereupon the brush 18 will further extend the conduc-' tor 0 of the calling line to the conduct'orz' of the. called line, and polarized relay 17 will thus be included between two sources of potential which may or which may not be difierent.

It will be) described hereinafter how upon the enei'g'ization of relay 17 in one direction a certain result will be accomplished. and how upon the energization of polarized relay 17in another direction or how upon the non-energization of relay 17 a different result will be accomplished. The result in one case will be the restriction oi the service, and in the other use will be the successful completion of the connection.

If a connection is made whereln' relay 17 is included in a circuit leading from a given potential to an equal potential. the result will bethe non-operation of relay 17 and the consequent establishment of the de sired connection. In this class will he calls which may be established from lines 1 to 41. from 2 to 3, from 3 to 2, from 4 to 5, from i to 1. and from 5 to 8.

If a connection is made whereby relay 17 is included in a circuit leading from a given potential to lower potential, then relay 1? will operate in one direction which will result in the establishment oi the desired connection. In this class will he calls which may be established from 1 to 1, from 1 to 2, from 1 to 3, from 1 to 5, from 2 to .1, from 2 to 2, from 2 to 5, from 3 to 1, from 3 to 5, from 5 to 1, from 5 to 2, and from 5 to 5.

If aconnection is made whereby relay 17 is included in a circuit leading from a given potential to a higher potential, then the operation of relay 17 will be in the opposite direction with the result that the desired connection will be barred. In this class will be calls which are attempted to be set up frcm lines 2 to 4. from S'to 3. from 3 to 1. from 4 to '2, from 4- to 3, from 1 to and from 5 to 4. v

In order to bring out these distinctions more clearly, two tables are given as follows. In the first table the possibilities of connectionsifrom lines in the first column to other lines areset forth, and in the second table possibilities of connections" being estab- Cancalll 2 3 5 Class 1 lines 7 Class 2 lines Class 3 lines Glass 4: lines Class 5 lines I Can be called 1 2 3 4 5 Class 1 lines Class 2 lines Glass 3 lines It Class 4 lines Class 5 lines calllines of any class of service whatsoever Line 2, representing class- 2 service, is restricted from calling a line provided with class 4; service but may call lines provided with any other class of service. According to the first table, lines provided withclass 2 service and class 5 service are apparently the same and the diflerence only appears when the second table is examined and it is seen that class 2 service difiers from class 5 service in that while class 5 service lines may be called by any other class ofservice lines, class 2 service lines are barred to class 4 service lines.

With this short description we will go to a description of the means employed in carrying out this invention.

Figs. 2 and 3 taken together, Fig.3 being placed below Fig. 2, represent a telephone system employing the present invention.

Here is illustrated an. intraoflice connection in an exchange having a small capacity. In general the connection is established in the manner set forth in the patent to Franke #1,268,106, granted June, 1918; that is a by-path connection between the calling and called lines is first established by means ofa numerical switch and then a talking connection is substituted by non-numerical'switches and the originally established by-pathis released. f I A Inthe drawings now under consideration two telephone lines 200and 201 are shown and a third 202, is indicated. ,Each telephone line has its individual line switch here shown as rotary step-by-step switches I having a normal position. Switch 203 is individual to line 200 and switch 20 1 is individual to line 201. Individual tothe line there is also a switch stepping magnetand a rela which acts as a combined line, test and cut ofi relay. Thus line 200 is provided with its individual switch magnet 205 and relay 206. Also individual to the line are three terminals in a' numerical switch byjmeans of which the line is identified as a-ca-lled line. Thus terminals 301, 302and 303 form ing a set and accessible respectively to brushes 300,304: and 305 are individual to line 200. Inlike manner, the set of terminals 311, .312 and 313 is individual to line 201 and the set of terminals 321, 322

and 3231s individual to line 202. Each line further has two class conductors in divldual to 1t, one known as theoutg'olng classconductor and the other known asthe incoming class conductor. Thus line 200 has conductor v207, line 201 has conductor 209, and line 202 has conductor 208 as its individual outgoing class conductor, and line 200 has conductor 31 1, line '201 has conductor 315 and line 202 has conductor 31 6 as its individual incoming class conductor.

In the 'manner described in connection with Fig. 1 there is provided, common to the lines'of the exchange a plurality of potential leads towhich the indiv'idualclass conductors of the different lines are connected in different combinations." Thus in Figfi 3' there are the four potential leads 306, 307, 308. and 309. Lead-306 is at zero potential, being connected to ground, lead 307 may be at twenty volts potential, lead vided with class 2 service according to the I classification explained in connection with Fig.1. In like manner leads 209 and 315,

individual to line 201 are connected to potential'leads 309 and 306 respectively and thus line 201 is provided with classl service. 'Line 202 is provided with class four service through the connection of its leads 208 and 316 to potential leads 306 and 309 respectively. 1 i 1 In'this system a line is marked as idle through the direct connection of ground to its terminal associated with-brush 304;and 'markecl as busy through the entire absence of ground potential or the connection of ground" through a resistance to the same terminal.- Thus line 201 shown in its idle condition is so markedthrough the maintenance of a connection from ground brush 213, conductor 215, terminal 312. At a certain stage of the operation of switch. 9

when brush 213 is on its second terlninal' conductor 215 will be free from ground and at this'stage a connectionbeing established to line 201'will be barred. Likewise when switch 204 is in. any otherposition a connection, which will beestablished in a manher to be hereinafterdescribed, will extend from ground, brush 213 any one of its terminals from the third on, the middle left hand armature and front contact of relay 216, resistance 217, conductor 215 and thence ['0 terminal 312 and in consequence whereof seeking connections will be barred.

When the subscriber at station 200 removes his receiver from its switchhook he will create a bridge across the line whereby a connection will be established from ground and battery, winding armature and back contact of magnet 205, switch brush 222 and its first contact, thence in series through the two windings of relay 206 the back contact and outer left hand armature of relay 206 through the loop of the line 200, inner left hand armature and back contact of relay 206 conductor 218, armature 310 and its back contact controlled by relay 318, back contact and inner left hand armature of relay 317 to ground. This connection results in the energization of relay 206,

and upon the energization of relay 206 and not until then, the energization of magnet 205. Due to the high resistance of the left hand winding of relay 206 only relay 206 can become energized in the circuit established by the removal of the receiver at the substation and thus relay 206 acts as a line relay. Upon the movement of the armatures of relay 206 a circuit is established from ground, battery, winding armature and back contact of magnet 205, brush 222 and its first contact, right hand low resistance winding of relay 206, inner right hand armature and front contact of relay 206 to ground whereby relay 206 is maintained energized although its original energizing circuit is opened at its-outer left hand armature. This circuit however now includes magnet 205 in a low resistance path and so magnet 205 becomes energized and thereby moves the brushes 220 to 224 inclusive onto their second contacts. Upon the energization of magnet 205 its energizing circuit is opened at its own back contact and therefore both magnet 205. and relay 206 become deenergized.

Now relay 206 becomes again energized in the original energizing circuit since the first and second contacts associated with brush 222 are connected together and so in the manner described magnet 205 will consequently be energized a second time and will move the brushes of switch 203 forward onto their third contacts. In a manner which will appear hereinafter if brush 222 does not at this point engage a terminal which has full battery potential thereon relay 206 will become deenergized. Assuming this to be the casethen a circuit will be established from ground, brush 223, any

one of its terminals including and from the.

third on, the middle-right hand armature and back contact of relay 206,1back contact,

armature and winding of magnet 205 to battery and ground. Magnet 205 being thus included in a self interrupting circuit will move the brushes forward stepby-step until brush 222 encounters a terminal having full battery potential thereon. At this time a circuit will be established from ground and battery back contact and left hand armature of relay 329, back contact and right hand armature of relay 225 resistance 226, conductor 227, brush 222, through the two windings in series ofrelay206 and thence over the original energizing circuit of relay 206. Relay 206 attracts its armatures and establishes itself in a locking circuit including its right hand low resistance winding, its inner right hand armature and front contact to ground.- Thus relay 206 performs the function of a test relay to determine the busy or idle condition of the connecting link. Having thus chosen the first idle link relay 206 becomes energized and stops the further movement of the brushes of switch 203 by opening the circuit for magnet 205 at the middle armature and back contact of relay 206. This relay now, by locking in a circuit extending into the selected link, performs the function of a cut off relay since at itsleft hand armatures it disconnects the line 200'from the original energizing circuit of relay 206 and extends the line to brushes 220 and 221. I I

An idle link circuit being now selected the line from station 200 is nowextended through the brushes 220 and221, through the windings of differential relay 227 and the left hand and middle windings of relay 228 to battery and, ground on the one hand and to ground on the other. Relay 227 being differentially wound does not become energized but relay 228 not being so wound does become energized whereupon a circuit is established from ground right hand armature and back Contact of relay 227 outer right hand armature and front contact of relay 228, winding of slow-to-release relay 229 to battery and ground. Relay 229 attracts its armatures and connects battery to resistance 226 independently of the armatures of relays 329 and 225 so as to maintain relay 206 energizedunder control of. the calling subscriber. Since relay 206 is now connected through its low resistance winding to conductor 227 and on account of the resistance 226 another hunting individual line switch will pass this point as busy because another relay 206 will not energize in parallel with the low resistance right hand winding of the relay 206 which is holding the connection.

The connection having now been extended to a link circuit will be further extended by means of a non-numerical switch indicated in Fig. 3 to the apparatus used in establishingv the by-path connection. In a system of this size two such connecting means may be supplied, one of which is indicated in full in Fig. 3 and the other of whichis indicated'in part in the small rectangle enclosed in the broken linesin the upper part of Fig. 3. The second of these is indicated for the purpose of showing the interrelation of the two and the several guards that are provided to prevent interference.

As will appear more fully hereinafter the motor magnets of the various non-numerical switches are connected in parallel. magnet 325 having control of brushes 330, 331, 332 and 333 is connected in parallel with motor magnet 324 having control of similar brushes in the second group'of apparatus. 7

l-Iereinbefore a circuit was traced through armature 310 of relay 318 to the inner left hand armature of relay 317' and thence to ground. Relays 317 and 318 are corresponding-relays in these two groups of apparatus and when either one is energized this circuit is opened and the line relays of other calling lines are prevented from operating at that'time. Relay 318, as will be seen hereinafter is a. controlling relay which is energized for a short interval of time during which it is necessary that further operations of the circuit be temporarily halted; Thus the outer left hand armature of relay 317 and armature '327 of relay 318 are connected in parallel and both connect ground to conductor 328' to cause the energization of relay 329.- Relay329 is a multi-contact relay controlling a plurality of leads equal in number tothe number of link circuits provided in this system. Thus the innermost left hand armature of relay; 329 is seen to be connected into the apparatus associated with thepair ticular link circuit here illustrated. In a similar manner the other armatures of'relay 329 may be connected into the apparatus of other link circuits, so that when either relay 318 or 317 is energized and consequently relay'329 is energized, the battery connection to the test contacts of all link circuits .is broken and the link "circuits'are marked during this instant as busy. 1

During the operation of'relay318. a circuit is established from ground, .the outer right hand armature of relay 318, through the right hand winding of relay 320 to battery and ground to maintain the energization of this relay. :In a similar manner during the energization of relay 317 a circuit is established from ground, the right hand armature of relay 317, the right hand winding of relay 319 to battery and ground to maintain the relay 319 energized during this interval. As will beseen hereafter, relay 319 controls an essential testing operation and since such testing operation must I Thus not be made while relay 317 for instance, of the secondgroup of apparatus-is operated,the operation of relay 317 provides means for holding up the testing o'peration in'thec-ircuitabove illustrated.

I It should be noted that the switch co1nprising wipers 330 to"333, inclusive is of that type having no normal position so that the wipers when once brought to rest remain at that 'point'until moved in consequence of another call: j

Upon the extension of the telephone line to the link circuit of Fig. 2 and the consequent energization'of relay 228, a circuit is established from ground through the right hand winding of relay 228, the inner right hand armature and front contact of relay 228, armature and .back contact of relay 231,

conductor 232, outer left hand armature and.

back contact of relay"334, back contact armatureandwindin of magnet'325 to battery and ground. As as been mentioned hereinbefore, magnet 324 is energized in parallel with magnet 325 but we will assume that magnet 325 is successful in bringing its brushes into contact with the calling line circuit first and thus establishing the required connection."*-The establishment of the circuit just described places magnet 325 in a self-interrupting circuit and hence this magnet will energize and deenergize in sequence and move the brushes 330' to 333,

inclusive, forward step by step. When the calling link circuit has been reached a circuit'will be established from battery, back contact and armature of release magnet 335, the two windings of relay 334 in series, brush 330 and its third .contact,"conductor 336,

outer left hand armature and back contact of relay 225, left hand winding of relay 230, front contact and inner left hand armature of relay 228, winding of relay 231, right 231 looks infa circuit from' ground. front contact and right hand armature of relay 229, winding of relay 231, front contact and left hand armature of relay 231, left hand winding ofrelay 230, back contact and outer left hand armature of relay 225 and thence tobattery through the left hand windingof relay 334'. In this'circuit relay 231 becomes energized independent of the inner left hand armature of relay 228 so that upon the/movement of this armature during the sending of impulses, relay 231 will? not be affected. The circuit is now in a stable 'conditien awaiting the sending of impulses from the calling substation.

In order to connect to station 201, two trains of impulses will be sent. These impulses are in the form of short interruptions at the calling subscribers loop circuit and they each result in the momentary deenergizatiorr of relay 228. a 1

At each backward movement of the armatures of relay 228, a circuit is established from ground, back contact and left hand armature of relay 227, outer left hand armature and back contact of relay 228, conductor 233, brush 332, left hand winding of relay 319, the inner right hand armature and front contact'of relay 334, the outer left hand armature, and back contact of relay 337, winding of primary magnet 338 to battery and ground. In this manner magnet 338 becomes successively energized a number of times and moves the brushes 300, 304 and 305 forward in a primary direction a corresponding number of steps. Upon the first movement of thebrushes 300, 304 and 305, the ofi-norrnal contact device 339 is actuated so that four pairs of contacts controlled thereby are all closed. At the end of this series ofimpulses and after a short interval slow-to-release relay 319 becomes deenergized whereupon a circuit is established from ground,'the right hand armature and back contact of relay 319, winding of relay 337, the uppermost pair of contacts of off-normal device 339 to battery. Relay 337 thus becomes energized and through-its inner left hand armature locks up in a circuit independent of the armature and contact of relay 319. Shortly thereafter the calling subscriber may send the second series of impulses whereupon magnet 340 will be energized instead of magnet 338 due to the switching of the circuit at the outer left hand armature of relay 337. Magnet 340 meves the brushes 300, 304 and 305 in a secondary direction a number of steps corresponding to the number of impulses in the train new sent out from the calling subscribers substation. In consequence thereof the brushes 300, 304 and'305 are moved to connection with terminals 311, 312 and 313, respectively.

It will be noted that relay 319 ;is slowto release and that it remains energized throughout the sending of a train of impulses. During the energization of relay 319, relay 341 is energized in a circuit extending from ground, the right hand armature and front contact of relay 319, winding of relay 341 to battery and ground. Relay 341 is also slow to release, therefore at the end of this last series of impulses, relay 319 will first become deenergized and relay 341 will retain its armatures in their actuated position for an instant thereafter. During this'instant a test circuit including the polari zed relay 343 hereinbefore mentioned is established. 7 7

At. the beginning of the description of thesetwo figures it was stated that station 200 was provided with class 2 service and that station 201 was provided with class 1 service and that therefore a connection could be established from one to the other. Thus in the present instance upon the release of relay: 319 and prior to the release of relay 341, a circuit is established from potential lead 308, resistance 342, conductor 207, front contact and outermost right hand armature of relay 206, brush 224, conductor 235, brush 333, back contact and left hand armature of relay 319, left hand armature and front contact of :relay 341, polarized relay 343, brush 305, terminal 313, resistance 344, potential lead 306. Since relay 343 is included in a circuit from a given potential of 60 volts to a loading potential of 01 volts and since this relay is arranged to respond only to current in a circuit from a lower to a higher potential, the establishment of the present circuit results inthe non-operation of relay 343. under the presentcondition would tend .to operate in. a clockwise direction but since it is normally held in this position it cannot 'move further and the net result is the non-operation of the relay.

Very shortly thereafter, relay 341 moves its armatures to their normal position whereupon a circuitis established from battery, the right hand armature and back contact of relay 341, back contact and next to the innermost right hand armature of relay 318, right hand winding of relay 345, brush 304, terminal 312, conductor 215, and. thence to the first terminal associated with brush 213. If station 201 is idle, as we will .assumexit to be, brush 213 will rest on this first terminal and thus complete the circuit to ground, whereupon test relay v345 will become energized. If, as hereinbefore described, brush 213 is at another position then the resistance 217 will be included in the circuit and the current flowing through the test circuit will be insufficient to cause the energization of relay 345. 7

Upon the energization of the test relay 345 a circuit is established from ground, the front contact and inner left hand armature of relay 345, winding of relay 318 and through the ofl-ncrmal contact device 339 to battery, whereupon relay 318 attracts its armatures and locks up in a circuit includ ing its inner right hand armature and front contact, thereby becoming independent of the continued energization of relay 345.

Several results of the energization of relay 318 have been given hereinbefore .and

The armature of relay 343 so will not be repeated at'thi'stime. Addi'-' tional results include'the removal of the short circuit about the le'ft handfh gh resistance windingof-relay345 at 'the' next to the innermost right hand armature and back contact of relay 3l8,"whereupon relay 345 mayreni'ain energized when resistance 217 is introduced into its circuit. Through the movement of its left hand armature, relay 318 connects battery "through the brush 331,. conductor 236, and thence through the left hand low resistance winding of relay 225 so as to raise thepotential of conductor 227 to the point where this link circuit may be seized by a hunting line switch. At'the same time in order to' prevent any other hunting 'line switch from seizing this cir cuit, relay 329 is energized in the manner hereinbefore describedto remove battery potential from all other idle link. circuits so that now among the' link circuits the particular one here is the onlyone which may be seized. Simultaneously, therewith,a circuit is establishedfrom ground,"armature 346, and its associated front contact,, brush 300, terminal 311, conductor 237, both Windings. of relay 216 inseries, brush 212 and its first contact, back contact, armature and winding of m'agnet'238 tobattery. The connection of groundto conductor, 237 causes the switch 204to' hunt in" the manner hereinbefore described in connection with switch 203 and since the'link circuit characterized by substantially full' battery potential on test wire227' is now the only oneavailable, switch 204 will inevitably come. to. rest on its terminals. I

As brush 213 passes on to itssecond contact the circuit for 're'la'y'345 is opened whereupon it releases its armatures." A circuit is now "established from g mafarmature 347 and its associated frontfcontact,

outermost left hand armature .andba'ck contact of relay 345, windingof relay 348, through the off-normal contactdevice. 3.39 to battery. Relay 348 becomes "energized in this circuit and locks up through flits from contact and innermost 'left hand armature independently of thev outermost left hand armature and relay 345. i

hen the line switch 2040f line 201 comes to rest on the terminals of the link'circuitinvolved in this-connection, cutofi' relay 216 will become permanently energized Whereupon a circuit Will be established from battery, right hand armature and back contact of relay 341, the left hand high resistance winding and right hand "low resistance Winding of relay 345,'brush 304 terminal 312, conductor 215, resistance 217, front contact and middleleft hand armature of relay 216, third contact and Wiper 213 to ground. The completion of this circuit is a signal that the connection has been completed between substation 200 and substation 201 and that the by path connection may be released. Hence relay 345 becomesenergized and establishes a eonnectionrrom ground front contact and outer left hand armature of relay 348, middle left "hand armature-and front contact of relay 345, Windingfof release'magnet'335 to battery. Magnet 335 becomes energized and returns the brushes 300, 304 and 305 to normal"and the off-normal device 339 opens its contacts "with the result that relays-337, 318,

energi'zation of magnet 335fneither of these relays become-again,energized. Thus relays 228, 229, .225 and 231 of the "link circuit-re main energized" all others are restored.

The called substation is signaled by the subscriber at substation 200 rapidly manipu- :lating his receiver hook or-by working his impulse dial. 4 The making and breaking of the'circuit including the source of talking current rapidly changes the-potential across the condenser at substation 201'aiid' the charge and discharge ofthis condenser causes the operation of the substationbell. This method ofsignaling the called subscriber has been found practice to be successful and although other methods may. be used in this 'f sy stem since this operation forms no part of the present invention-then for the sake of simplicity such otherfniethods' will not be .clescribea A When called party answers talking 7 current "forflbothparties is supplied through the windings of relay 228. At the end of the conversation when both parties hang up their receivers relay 228 becomes deenergized and "this is followed by the deenergization of relays; 229,231 and 225. Battery beingremoved fromconductor 227', '2'16return' to normal. y 'circuitfisno'westablished from battery (winding, armature and back contact of magme e205, back contact and middle right hand "armature of relay 206 brush 223 to ground ,Wl IGI GLl POH: magnet 205 will drive the brushes 220 to224 completely around until they reach "normal position when brush circuit above described.

; In a similarimanner switch 204 is returned I'Irainannereiitirely similar-to that herein described a successful connection can be established between station 201 as a calling station and station 200 as a called station. Under such a condition the circuit for relay relays 206 and i i 115 223 opens the 343 would extend from potential lead 309,

resistance 349, conductor 209, front contact and outer left hand armature of relay 216, brush 214 and its third contact, conductor 235, brush 333, back contact and left hand armature of relay 319, front contact and left hand armature of relay 341, relay 343, brush 305, terminal 303 (individual to line 200), conductor 314, resistance 350, to potential lead 307. Under this condition relay 343 is included in a circuit from ahigher potential (60 volts) to a lower potential (20 volts) and hence will not operate.

If however, a call is attempted from substation 200 to line 202 relay 343 will b included in a circuit from potential lead 308, resistance 342, conductor 207, front contact and outer right hand armature of relay 206, brush 224 and its third contact conductor 235, brush 333, back contact and left hand armature of relay 319, left hand armature and front contact of relay 341, relay 343, brush 305 terminal 323 (individual to line 202) conductor 316 resistance 351 to potential lead 309 and since relay 343 is now included in a circuit from a lower potential (40 volts) to a higher potential (60 volts) it becomes energized. This has two results; first a connection is established from ground armature and contact of relay 343, secondary winding of busy tone transformer 352 front cont-act and outer left hand armature of relay 334, conductor. 232 back contact and right hand armature of relay 231, front contact, inner right hand armature, and right hand winding of relay 228 to ground, whence by induction busy tone is transmitted to the calling station to apprise the subscriber thereat that a connection to line 202 cannot be had. Secondly the energization of relay 343 results in the establishment of a connection from ground, armature and front contact of relay 343 winding of release magnet 335 whereupon the release of the common apparatus takes place as before described.

Should a connection be set up between line 202 and line 200, relay 343 will be included in a circuit from conductor 306, resistance 353, conductor 208, brush 234, conductor 235, brush 333, back contact and left hand armature of relay 319-, left hand armature and front contact of relay 341, relay 343, brush 305, terminal 303 (individual to line 200) conductor 314, resistance 350 to potential lead 307, whereupon relay 343 will become energized with the same results hereinbefore described.

Where the called line is found busy relay 345 fails to operate as hereinbefore set forth. As a result relay 318 remains unoperated and the line switch of the called line is not disturbed. The calling subscriber will after a while hang up his receiver thereby directly causing the deenergization of relay 228and indirectly causing the deenergization of relay 334. The deenergization of the latter relay establishes a circuit from ground, battery, winding of release magnet 335, back contactand outer right hand armature of relay 334, lowermost contact of off normal. device 339 to ground. The release magnet is energized and the connection is broken down in the manner hereinbefore described.

\Vhat is claimed is:

1. In a telephone system, a plurality of common conductors each connected to a source of current of a different potential, telephone lines, each said line having connection to a plurality of said common conductors to characterize said line as entitled to a specific class of service, means for interconnecting said lines and means included therein responsive to a connection including a source of current connected to the calling line and a source of current connected to the called line for determining the class of service between said lines.

2. In a telephone system, a plurality of common conductors each connected to a source of current of a different potential, telephone lines, each said line having connection to a plurality of said common conductors to characterize said line as entitled to outgoing service of a particular nature and incoming service of a particular nature, means for interconnecting said lines and means included therein responsive to a connection including a source of current connected to the calling line and a source of current connected to the called line for determining the class of outgoing service of the calling line and the class of incoming service of the called line.

3. In a telephone system, a plurality of sources of current each of a different potential, telephone lines, each said'line having connection to certain of said sources of current to characterize said line as entitled to a definite class of service, means for interconnecting a calling and a called line and a relay included in said means responsive only to a connection fro-m a source of current of a lower potential connected to said calling line to a source of current of a higher potential connected to said called line for preventin the interconnection of said calling and calle lines.

In witness whereof, I hereunto subscribe my name this twenty-eighth day of April,

FRITZ LUBBERGER. 

